U.S. patent number 6,483,235 [Application Number 09/365,888] was granted by the patent office on 2002-11-19 for image display apparatus with rectangular-shaped spacers having added tensions.
This patent grant is currently assigned to Sony Corporation. Invention is credited to Yukinobu Iguchi, Shinji Kanagawa.
United States Patent |
6,483,235 |
Iguchi , et al. |
November 19, 2002 |
**Please see images for:
( Certificate of Correction ) ** |
Image display apparatus with rectangular-shaped spacers having
added tensions
Abstract
To prevent lowering of the brightness of a displayed image,
realize satisfactory strength against high pressure and reliably
form spacers, an image display apparatus incorporates an anode
substrate having a structure in which at least an image display
portion is formed on a first substrate; a cathode substrate in
which at least an electron emission units are formed on a second
substrate and which is disposed opposite to the anode substrate;
and spacers each of which formed into a substantially rectangular
shape and which are stood erect between the anode substrate and the
cathode substrate, wherein the two long sides of the spacer are
secured to at least either of the anode substrate or the cathode
substrate, and tensions are added to the spacers in the lengthwise
direction of the spacers.
Inventors: |
Iguchi; Yukinobu (Kanagawa,
JP), Kanagawa; Shinji (Kanagawa, JP) |
Assignee: |
Sony Corporation
(JP)
|
Family
ID: |
16753337 |
Appl.
No.: |
09/365,888 |
Filed: |
August 3, 1999 |
Foreign Application Priority Data
|
|
|
|
|
Aug 4, 1998 [JP] |
|
|
10-220588 |
|
Current U.S.
Class: |
313/495; 313/257;
313/292 |
Current CPC
Class: |
H01J
31/127 (20130101); H01J 29/864 (20130101); H01J
9/242 (20130101); H01J 2329/866 (20130101); H01J
2329/8665 (20130101); H01J 2329/8625 (20130101); H01J
2329/8655 (20130101); H01J 2329/863 (20130101) |
Current International
Class: |
H01J
29/02 (20060101); H01J 001/62 (); H01J
063/04 () |
Field of
Search: |
;313/495,257,292,258,422 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Patel; Vip
Assistant Examiner: Quarterman; Kevin
Attorney, Agent or Firm: Rader, Fishman & Grauer PLLC
Kananen, Esq.; Ronald P.
Claims
What is claimed is:
1. An image display apparatus comprising: an anode substrate having
a structure in which at least an image display portion is formed on
a first substrate; a cathode substrate in which at least electron
emission units are formed on a second substrate and which is
disposed opposite to said anode substrate; and a plurality of
spacers, each of which is formed into a substantially rectangular
shape and which are stood erect between said anode substrate and
said cathode substrate, wherein two long sides of each of said
spacers are secured to at least either of said anode substrate or
said cathode substrate, wherein said spacers are formed at a
predetermined tension in a direction lengthwise of said spacers,
wherein a thermal expansion coefficient of said spacer is defined
.alpha.s, a thermal expansion coefficient of said anode substrate
or said cathode substrate on which said spacer stands erect is
defined as .alpha.g, a difference between a temperature of said
spacer at which said spacer is stood erect and a temperature of
said substrate when said spacer stands erect is defined as
.DELTA.t1, a difference between a temperature at which said spacer
is heated after said spacer has been stood erect and the
temperature of said substrate when said spacer stands erect is
defined as .DELTA.t2, a difference between a lowest temperature at
which preservation is permitted and a temperature of said substrate
when said spacer stands erect is defined as .DELTA.t3 and a maximum
thermal expansion coefficient of said spacer within limit of
pulling is .epsilon., and wherein if .alpha.s.ltoreq..alpha.g, the
following expression are satisfied:
2. An image display apparatus according to claim 1, wherein a
thermal expansion coefficient of said spacer is defined .alpha.s, a
thermal expansion coefficient of said anode substrate or said
cathode substrate on which said space stands erect is defined as
.alpha.g, a difference between a temperature of said spacer at
which said spacer is stood erect and a temperature of said
substrate when said spacer stands erect is defined as .DELTA.t1, a
difference between a temperature at which said spacer is heated
after said spacer has been stood erect and the temperature of said
substrate when said spacer stands erect is defined as .DELTA.t2, a
difference between a lowest temperature at which preservation is
permitted band a temperature of said substrate when said spacer
stands erect is defined as .DELTA.t3 and a maximum thermal
expansion coefficient of said spacer within limit of pulling is
.epsilon., and wherein if .alpha.s.ltoreq..alpha.g, the following
expression are satisfied:
3. An image display apparatus according to claim 1, further
comprising: said anode substrate has red-, green-, and blue-light
fluorescent emission members formed on predetermined anode
electrodes in an alternating stripe configuration.
4. An image display apparatus according to claim 1, further
comprising: said cathode substrate incorporates a plurality of
spindt-type electron emission units in a matrix configuration.
5. An image display apparatus according to claim 4, wherein each
electron emission unit further comprises: an insulating substrate;
a cathode electrode formed on said insulating substrate; a conical
emitter electrode formed on said cathode electrode; a gate
electrode disposed apart from the emitter electrode by a
predetermined distance and laminated through the cathode electrode
and an insulating layer.
6. An image display apparatus according to claim 3, further
comprising: cathode electrodes formed into an alternating stripe
configuration in parallel with the anode electrodes and the
fluorescent members.
7. An image display apparatus according to claim 1, further
comprising: said spacers are secured to either the anode or cathode
substrate with an ultraviolet curing adhesive agent, and are
uniformly disposed in the plane of the image display portion.
8. An image display apparatus according to claim 1, further
comprising: an outer wall is joined to the cathode and anode
substrates through frit glass.
9. An image display apparatus according to claim 1, further
comprising: a space between the cathode and anode substrates is
maintained at a predetermined degree of vacuum.
10. An image display apparatus according to claim 9, further
comprising: said vacuum is maintained through use of an exhaust
pipe and a gas absorber.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image display apparatus
incorporating paired anode substrate and cathode substrate disposed
opposite to each other through a spacer and a manufacturing method
therefor, and more particularly to an image display apparatus
incorporating electron emission units for emitting field electrons
and a manufacturing method therefor.
2. Description of the Related Art
In recent years research and development of an image display
apparatus have been performed to reduce the thickness of the
display unit. Under the present circumstance, a field emission type
display apparatus (hereinafter abbreviated as "FED") incorporating
so-called electron emission units has received special
attention.
The FED incorporates a cathode substrate having the electron
emission unit and an anode substrate having a fluorescent layer and
disposed opposite to the cathode substrate. In general, the
electron emission units of the cathode substrate are spindt type
electron emission units or flat electron emission units. The anode
substrate incorporates an anode electrode which is formed below the
fluorescent layer and to which anode voltage for accelerating
electrons emitted from the electron emission unit is applied.
In the FED, a vacuum state is maintained between the cathode
substrate and the anode substrate. Therefore, the cathode substrate
and the anode substrate are applied with high pressure from the
atmosphere.
Therefore, there is apprehension that the high pressure will cause
the cathode and anode substrates disposed opposite to each other to
be warped and broken. To prevent the foregoing problem, the FED has
been structured such that the thickness of each of the cathode
substrate and the anode substrate is enlarged to obtain
predetermined strength against high pressures. When a FED having a
width across corners of 5 inches is manufactured, a glass substrate
having a thickness of about 5 mm is required. When a FED having a
width across corners of 10 inches is manufactured, a glass
substrate having a thickness of about 10 mm is required. Therefore,
a FED having a light weight and small thickness cannot be
manufactured.
It might therefore be feasible to employ thin glass substrates each
having a thickness of, for example, 1.1 mm to manufacture a cathode
substrate and an anode substrate. Moreover, spacers are disposed
between the cathode substrate and the anode substrate. Thus,
strength against the high pressure caused from the atmosphere is
realized. The spacers are exemplified by bead spacers randomly
disposed between the cathode substrate and the anode substrate;
cylindrical spacers disposed in ineffective pixel regions between
the cathode substrate and the anode substrate, and columnar or wall
shaped spacers formed between the cathode substrate and the anode
substrate by printing or photolithography.
When the bead spacers are employed, the portions in which the bead
spacers are formed are made to be ineffective regions. Thus, the
brightness of a formed image is lowered. When the distance between
the cathode substrate and the anode substrate is elongated to
improve electricity resistance between the cathode substrate and
the anode substrate, the bead spacers must be enlarged. Hence it
follows that the ineffective regions are undesirably enlarged. That
is, when the bead spacers are employed, there arises a problem in
that the elongation of the distance between the anode substrate and
the cathode substrate causes the ineffective regions to undesirably
be enlarged.
When columnar spacers are disposed, a plurality of spacers each
having a high aspect ratio (height/diameter) are disposed.
Therefore, satisfactory strength against high pressure cannot
easily be obtained.
When the columnar or wall-shape spacers are employed, the foregoing
spacers cannot easily be formed between the cathode substrate and
the anode substrate, that is, in a space having a small height of
about 1 mm to about 2 mm by printing or photolithography.
As described above, the conventional FED encounters a difficulty in
reliably forming a spacer which does not lower the brightness of a
displayed image and which has sufficient strength against high
pressure. To overcome the foregoing problem, a structure in which a
plate-like spacer is disposed has been disclosed in U.S. Pat. No.
564,847. The plate-like spacer is received between rail-like spacer
guides provided for the cathode substrate and the anode
substrate.
Therefore, spacer guides each having a high aspect ratio must
precisely be provided for the cathode substrate and the anode
substrate to dispose the plate-like spacer. However, the precise
spacer guides each having the high aspect ratio cannot easily be
provided for the cathode substrate and the anode substrate.
Therefore, the method disclosed in U.S. Pat. No. 564,847 has a
problem in that the spacer cannot easily and reliably be
formed.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide an
image display apparatus which is capable of overcoming the
foregoing problems experienced with the conventional electron
emission units, which does not lower the brightness of the
displayed image, which has sufficient strength against high
pressure and which permits a spacer to reliably be formed and a
manufacturing method therefor.
To achieve the foregoing object, according to one aspect of the
present invention, there is provided an image display apparatus
comprising: an anode substrate having a structure in which at least
an image display portion is formed on a first substrate; a cathode
substrate in which at least electron emission units are formed on a
second substrate and which is disposed opposite to the anode
substrate; and spacers each of which is formed into a substantially
rectangular shape and which are stood erect between the anode
substrate and the cathode substrate, wherein two long sides of the
spacer are secured to at least either of the anode substrate or the
cathode substrate, and tensions are added to the spacers in the
lengthwise direction of the spacers.
The image display apparatus according to the present invention and
structured as described above incorporates the spacer stood erect
between the anode substrate and the cathode substrate and capable
of maintaining a predetermined distance between the anode substrate
and the cathode substrate. The spacer of the image display
apparatus is formed into a substantially rectangular shape.
Tensions are added in a lengthwise pulling direction of the
spacers, that is, in the lengthwise direction in which the spacer
is elongated. Therefore, the spacer of the image display apparatus
is able to prevent distortion and fracture even if the spacer is
subjected to heat treatment.
To achieve the foregoing object, according to another aspect of the
present invention, there is provided a method of manufacturing an
image display apparatus having a structure that an anode substrate
having a structure in which at least an image display portion is
formed on a first substrate and a cathode substrate in which at
least electron emission units are formed on a second substrate are
disposed opposite to each other through spacers each of which
formed into a substantially rectangular shape, the method of
manufacturing an image display apparatus comprising the steps of:
securing the two long sides of the spacers to at least either of
the anode substrate or the cathode substrate, wherein tensions are
added to the spacers in the lengthwise direction of the
spacers.
The method of manufacturing an image display apparatus according to
the present invention is structured such that the spacers are
disposed between the anode substrate and the cathode substrate so
that the cathode substrate and the anode substrate are disposed
opposite to each other. The foregoing method is structured such
that the spacers are secured in a state in which predetermined
tensions are added in the lengthwise pulling direction of the
spacer, that is, in a direction in which the spacer is elongated in
the lengthwise direction. Therefore, the method according to the
present invention is able to dispose the spacers without occurrence
of distortion and fracture.
Other objects, features and advantages of the invention will be
evident from the following detailed description of the preferred
embodiments described in conjunction with the attached
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic perspective view showing the structure of a
FED which is an example of an image display apparatus according to
the present invention;
FIG. 2 is a cross sectional view showing an essential portion of an
electron emission unit formed on the cathode substrate;
FIG. 3 is a schematic view showing the positions of spacers;
FIG. 4 is a vertical cross sectional view showing an essential
portion of the image display apparatus according to the present
invention;
FIG. 5 is a vertical cross sectional view showing an essential
portion of the image display apparatus according to the present
invention;
FIG. 6 is a perspective view showing a state in which the spacer
has been joined to a jig which is used when the spacer is secured
to the cathode substrate;
FIG. 7 is a cross sectional view showing an essential portion of a
state in which the cathode substrate has been secured to the
spacer;
FIG. 8 is a cross sectional view showing an essential portion
essential portion of a state in which a protective film has been
formed on an adhesive agent;
FIG. 9 is a cross sectional view showing an essential portion of
each of the spacer and the cathode substrate in a case where an
inorganic adhesive agent is employed; and
FIG. 10 is a graph showing the relationship between temperatures at
which the zirconia spacer is heated and amounts of distortion of
the spacer.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Embodiments of an image display apparatus according to the present
invention and a manufacturing method therefor will now be described
with reference to the drawings.
As schematically shown in FIG. 1, electron emission units according
to this embodiment is adapted to a field electron emission display
which is a so-called FED (Field Emission Display). The FED
incorporates a cathode substrate 2 having electron emission units 1
arranged to emit field electrons and disposed in a matrix
configuration; an anode substrate 4 disposed opposite to the
cathode substrate 2 and having anode electrodes 3 formed into
stripe configuration and spacers 5 disposed between the cathode
substrate 2 and the anode substrate 4.
The FED has a structure that a space between the cathode substrate
2 and the anode substrate 4 is a high vacuum state.
In the FED according to this embodiments, pressure caused from the
atmosphere is exerted in a direction in which the cathode substrate
2 and the anode substrate 4 are joined to each other. However, the
FED according to this embodiment has the spacers 5 stood erect
between the cathode substrate 2 and the anode substrate 4 so that
the cathode substrate 2 and the anode substrate 4 are disposed
opposite to each other and apart from each other for a
predetermined distance against the foregoing pressure.
The anode substrate 4 of the FED according to this embodiment has a
structure that a red-light emission member 6R for emitting red
light is formed on a predetermined anode electrode 3. A green-light
emission member 6G for emitting green light is formed on an
adjacent anode electrode 3. A blue-light emission member 6B for
emitting blue light is formed on an adjacent anode electrode 3.
That is, the anode substrate 4 has the red-light emission member
6R, the green-light emission member 6G and the blue-light emission
member 6B (hereinafter collectively and simply called "fluorescent
members 6") which are formed into alternating stripe shape.
The cathode substrate 2 of the FED according to this embodiment
incorporates a plurality of electron emission units 1 disposed in a
matrix configuration. As shown in FIG. 2, the electron emission
units 1 are so-called spindt-type electron emission units. Each
electron emission units 1 incorporates an insulating substrate 7
made of glass or the like; a cathode electrode 8 formed on the
insulating substrate 7; a conical emitter electrode 9 formed on the
cathode electrode 8; and a gate electrode 11 disposed apart from
the emitter electrode 9 for a predetermined distance and laminated
through the cathode electrode 8 and the insulating layer 10. The
FED has the cathode electrode 8 formed into a stripe configuration
in parallel with the anode electrode 3 and the fluorescent members
6. Moreover, a gate electrode 11 is formed into a stripe
configuration in a direction perpendicular to the cathode electrode
8. The FED according to this embodiment has the electron emission
units 1 formed at intersections between the cathode electrodes 8
and the gate electrodes 11. Therefore, the FED according to this
embodiment has the electron emission units 1 disposed in the matrix
configuration.
When the electron emission units 1 are manufactured, a plurality of
small openings 12 which penetrate the gate electrode 11 and the
insulating layer 10 are formed in the intersections regions formed
in the matrix configuration. That is, when the electron emission
units 1 are manufactured, the plural openings 12 are formed in such
a manner that the cathode electrode 8 is exposed in the bottom
portion. Then, a thin film made of a discharge material is formed
in the opening 12 from a diagonal position by evaporation or the
like so that a conical emitter electrode 9 is formed.
The FED according to this embodiment has pixels each of which is
constituted by the fluorescent members 6 in the three colors and
the electron emission units 1 disposed opposite to the fluorescent
members 6 in the three colors. In the FED, the pixels constituted
as described above are disposed in the matrix configuration.
Each of the spacers 5 of the foregoing FED is formed into a
substantially rectangular shape such that the spacers 5 are stood
erect between the anode substrate 4 and the cathode substrate 2. At
this time, the spacers 5 are temporarily joined to either of the
cathode substrate 2 or the anode substrate 4. In this embodiment,
the spacers 5 are joined to the cathode substrate 2. The procedure
is not limited to the foregoing method. As a matter of course, the
spacers 5 may be joined to the anode substrate 4. Specifically, the
spacers 5 are joined between the electron emission units 1 disposed
in the matrix configuration, as shown in FIG. 3. Namely, the
spacers 5 are disposed between pixels structured as described
above, that is, in the ineffective pixel regions. In the FED
according to this embodiment, it is preferable that a plurality of
the spacers 5 are uniformly disposed in the plane of the
screen.
As shown in FIGS. 4 and 5, the spacers 5 are secured such that the
two long sides of the spacers 5 are bonded to the cathode substrate
2 with adhesive agent. As indicated with an arrow a shown in FIG.
4, tensions are added to the spacer 5 in a lengthwise pulling
direction. As shown in FIGS. 4 and 5, the cathode substrate 2 and
the anode substrate 4 maintain a predetermined distance through an
outer wall 18. The outer wall 18 has substantially the same shape
as the shape of each of the cathode substrate 2 and the anode
substrate 4. The outer wall 18 is joined to the cathode substrate 2
and the anode substrate 4 through frit glass 19. Therefore, the FED
has a structure that the cathode substrate 2, the anode substrate
4, the outer wall 18 and the frit glass 19 prevent leakage of air
from the inside portion of the FED.
To maintain a predetermined degree of vacuum in the FED, the FED
has an exhaust pipe 20 which is connected to a vacuum exhausting
apparatus (not shown). A gas adsorber 21 is disposed in the exhaust
pipe 20. Thus, the vacuum exhausting apparatus (not shown) is
joined to the FED through the exhaust pipe 20 so that the internal
space formed by the cathode substrate, the anode substrate and the
outer wall 18 is made to be a vacuum state. After the vacuum state
has been realized, the gas adsorber 21 adsorbs gas component left
in the foregoing internal space so as to maintain a high vacuum
state in the internal space.
When the spacer 5 is stood erect on the cathode substrate 2, the
temperature of the spacer 5 is made to be higher than the
temperature of the cathode substrate 2. Then, the two long sides of
the spacer 5 are secured to the cathode substrate 2. Namely, the
temperature of the spacer 5 is made to be higher than the
temperature of the cathode substrate 2 so that the spacer 5
expanded with heat is secured to the cathode substrate 2. When the
temperature of the spacer 5 and that of the cathode substrate 2
have been made to be substantially the same after the securing
process, the spacer 5 is contracted. As a result, the spacer 5 is
secured to the cathode substrate 2 in a state in which tensions are
added in the lengthwise pulling directions.
Specifically, a jig 25 structured as shown in FIG. 6 is used to
secure the spacer 5 to the upper surface of the cathode substrate
2. The jig 25 is made of a material, such as metal, having high
heat conductivity. The jig 25 has a groove 26 for receiving the
spacer 5 and a heater 27 for heating the inserted spacer 5.
As shown in FIG. 6, the jig 25 is heated by the heater 27 in a
state in which the spacer 5 has been inserted into the groove 26.
Thus, the spacer 5 is heated to a predetermined level.
Specifically, it is preferable that the jig 25 heats the inserted
spacer 5 to a level which is higher than the temperature of the
cathode substrate 2 by about 10.degree. C. to about 100.degree. C.
At this time, the spacer 5 is expanded because the spacer 5 has
been heated to the predetermined level.
In a state in which the predetermined temperature of the spacer 5
is maintained, the cathode substrate 2 having an adhesive agent 28
allowed to adhere to predetermined positions thereof and the spacer
5 are accurately positioned and brought into contact with each
other, as shown in FIG. 7. That is, the spacer 5 expanded owing to
heat is secured to the surface of the cathode substrate 2. It is
preferable that the adhesive agent 28 is an ultraviolet curing
adhesive agent. When the ultraviolet curing adhesive agent is
employed, the adhesive agent 28 can easily be cured by applying
ultraviolet rays after the cathode substrate 2 and the spacer 5
have been brought into contact with each other. Therefore, use of
the ultraviolet curing adhesive agent facilitates bonding of the
cathode substrate 2 and the spacer 5.
Then, as shown in FIG. 8, the spacer 5 is removed from the jig 25,
and then a protective film 29 is formed to cover the adhesive agent
28. It is preferable that the protective film 29 is made of a heat
resisting inorganic adhesive agent. Since the protective film 29
covers the adhesive agent 28, the spacer 5 can reliably be secured
to the cathode substrate 2 if the adhesiveness of the adhesive
agent 28 is deprived owing to heat treatment which will be
performed later.
When the spacer 5 and the cathode substrate 2 are bonded to each
other, only an inorganic adhesive agent 30 may be employed, as
shown in FIG. 9. It is preferable that the inorganic adhesive agent
30 is an agent which is cured in a short time owing to application
of a laser beam or the like which, therefore, is capable of
reliably bonding the spacer 5 and the cathode substrate 2 to each
other. The adhesiveness of the inorganic adhesive agent 30 of the
foregoing type is not deprived if the heat treatment is performed
afterwards. Thus, the spacer 5 and the cathode substrate 2 can
reliably be bonded to each other.
As described above, the temperature of the spacer 5 is higher than
that of the cathode substrate 2. In the foregoing state, the spacer
5 is secured to the cathode substrate 2. Thus, predetermined
tensions can be applied in the lengthwise direction of the spacer 5
after the temperatures of the spacer 5 and the cathode substrate 2
have been made to substantially be the same. That is, the foregoing
method enables the spacer 5 to be secured to the cathode substrate
2 in the state in which the predetermined tensions are added in the
lengthwise direction of the spacer 5.
Similarly, a plurality of the spacers 5 are sequentially secured to
the cathode substrate 2 in a manner not shown. Thus, the plural
spacers 5 can be stood erect at predetermined regions.
The present invention is not limited to the foregoing method of
standing erect the spacers 5 on the cathode substrate 2. For
example, the spacers 5 may be secured to the cathode substrate 2
which has been cooled. That is, the cathode substrate 2 is cooled
so as to be contracted, and then the spacers 5 are secured to the
contracted cathode substrate 2. When the temperature of the cathode
substrate 2 and the temperature of the spacers 5 have been made to
be substantially the same after the securing process, the cathode
substrate 2 is expanded owing to heat. Thus, the foregoing tensions
are added in the lengthwise direction of the spacers.
The FED structured as described above incorporates the plate-like
spacers 5 which are disposed to maintain a predetermined distance
between the cathode substrate 2 and the anode substrate 4 against
high pressure generated owing to the atmosphere. If the cathode
substrate 2 and the anode substrate 4 of the FED comprise thin
glass substrates, fracture of the FED occurring owing to the
foregoing pressure can reliably be prevented. That is, the FED
according to the present invention is able to employ thin glass
substrates. Therefore, the thickness of the FED can be reduced as
compared with a conventional FED.
Since the tensions are added in the lengthwise direction of the
spacers 5, the spacers 5 can be disposed without distortion.
Therefore, the accuracy of the positions of the two ends of the
spacers 5 which are secured to the cathode substrate 2 can be
improved. As a result, undesirable covering of the electron
emission unit 1 with the spacer 5 can be prevented. Thus, an
excellent accuracy of the positions can be improved. Therefore, the
foregoing FED is able to prevent undesirable exposure of the spacer
5 to the effective pixel region. Hence it follows that satisfactory
brightness of a displayed image can be maintained.
An assumption is made that a spacer 5 made of zirconia (having a
Young's modulus of 210 GPa) having the thermal expansion
coefficient .alpha.s of 100.times.10.sup.-7 is heated to 60.degree.
C., followed by securing the spacer 5 to the cathode substrate 2,
the temperature of which is 20.degree. C. In the foregoing state,
the extension coefficient .beta. of the spacer 5 can be obtained as
(100.times.10.sup.-7).times.(60-20) from
.beta.=.alpha.s.times..DELTA.t (.DELTA.t is a variation which takes
place owing to the temperature). The stress of the tension which is
added to the spacer 5 secured to the cathode substrate 2 is
8.4.times.10.sup.7 (Pa) according to the Hooke's law T=E.epsilon.
(E is a Young's modulus and E is an extension coefficient). As
described above, the spacer 5 made of zirconia is added with the
tension 8.4.times.10.sup.7 (Pa). Therefore, deviation of the
position of the spacer 5 can be prevented.
The foregoing FED is sometimes subjected to heat treatment. If the
thermal expansion coefficient of the spacer 5 and that of the
cathode substrate 2 are different from each other, there is
apprehension that the heat treatment causes the spacer 5 to be
distorted during the heat treatment or the spacer 5 is broken. In
general, if the spacer 5 and the cathode substrate 2 encounter
different expansion or contraction owing to heat during a
predetermined change in the temperature, the difference in the
expansion or contraction owing to heat results in the spacer 5
being distorted or the spacer 5 being broken.
The foregoing FED is sometimes subjected to a cooling test. That
is, the temperature of the FED is made to be a level not higher
than a so-called guaranteed temperature to evaluate the
characteristics of the FED. If the thermal expansion coefficient of
the spacer 5 and that of the cathode substrate 2 are different from
each other, there is apprehension that the cooling test causes the
spacer 5 to be distorted or the spacer 5 to be broken.
Therefore, the foregoing FED is structured such that the following
factors are controlled to satisfy predetermined conditions: thermal
expansion coefficient of the spacer 5, the thermal expansion
coefficient of the cathode substrate 2, the temperature at which
the spacer 5 is stood erect, the temperature to which the spacer 5
is heated after the spacer 5 has been stood erect and the
temperature of the spacer 5 to which the spacer 5 is cooled after
the spacer 5 has been stood erect. Thus, distortion and breakage of
the spacer 5 can reliably be prevented.
Assumptions are made that the thermal expansion coefficient of the
spacer 5 is .alpha.s, the thermal expansion coefficient of the
cathode substrate 2 is .alpha.g, (temperature at which the spacer 5
is stood erect)-(temperature of the cathode substrate 2 when the
spacer 5 is stood erect) is .DELTA.t1, (temperature to which the
spacer 5 is heated after the spacer 5 has been stood
erect)-(temperature of the cathode substrate 2 when the spacer 5 is
stood erect) is .DELTA.t2 and (temperature to which the spacer 5 is
cooled after the spacer 5 has been stood erect)-(the temperature of
the cathode substrate 2 when the spacer 5 is stood erect) is
.DELTA.t3. Another assumption is made that the maximum thermal
expansion coefficient of the spacer 5 within limit of pulling is
.epsilon..
If .alpha.s.ltoreq..alpha.g, it is preferable that the following
expression are satisfied:
If .alpha.s.gtoreq..alpha.g, it is preferable that the following
expressions are satisfied:
When the thermal expansion coefficient of the spacer 5 is not
higher than that of the cathode substrate 2 (when
.alpha.s.ltoreq..alpha.g), heating causes the cathode substrate 2
to furthermore be expanded. On the other hand, the spacer 5 is
relatively contracted. As a result, the spacer 5 secured to the
cathode substrate 2 is added with a tension in the pulling
direction. In the foregoing case, cooling causes the cathode
substrate 2 to furthermore be contracted. On the other hand, the
spacer 5 is relatively expanded. As a result, the spacer 5 secured
to the cathode substrate 2 is added with a tension in the
contracting direction.
When the thermal expansion coefficient of the spacer 5 is not lower
than that of the cathode substrate 2 (when
.alpha.s.gtoreq..alpha.g), heating causes the spacer 5 to
furthermore be expanded. On the other hand, the cathode substrate 2
is relatively contracted. As a result, the spacer 5 secured to the
cathode substrate 2 is added with a tension in the contracting
direction. In the foregoing case, cooling causes the spacer 5 to
furthermore be contracted. On the other hand, the cathode substrate
2 is relatively expanded. As a result, the spacer 5 secured to the
cathode substrate 2 is added with a tension in the pulling
direction.
In the expressions (1), (2), (3) and (4), expression
".alpha.s.times..DELTA.t1" indicates tension exerted on the spacer
5 when the spacer 5 is secured. Expression
"(.alpha.g-.alpha.s).times..DELTA.t2" indicates an amount of
expansion/contraction of the spacer 5 occurring after heating has
been performed and caused from the difference in the thermal
expansion coefficient of the spacer 5 and that of the cathode
substrate 2. Expression "(.alpha.g-.alpha.s).times..DELTA.t3"
indicates an amount of expansion/contraction of the spacer 5
occurring after cooling has been performed and caused from the
difference in the thermal expansion coefficient of the spacer 5 and
that of the cathode substrate 2. Therefore, the expression (1)
shows a requirement that a total of the tensions in the pulling
direction added to the spacer 5 when heating is performed must be
smaller than the thermal expansion coefficient .epsilon. within the
limit of the tensile strength of the spacer 5. When the expression
(1) is satisfied, breakage of the spacer 5 during heating can
reliably be prevented.
The expression (2) shows a requirement that the tension in the
contracting direction which is added to the spacer 5 when cooling
is performed must be smaller than the tension exerted when the
spacer 5 is secured. When the expression (2) is satisfied,
distortion of the spacer 5 during cooling can reliably be
prevented.
The expression (3) shows a requirement that the tension in the
contracting direction which is added to the spacer 5 is smaller
than the tension exerted when the spacer 5 is secured. When the
expression (3) is satisfied, distortion during heating can reliably
be prevented.
The expression (4) shows a requirement that a total of the tensions
in the pulling direction which are added to the spacer 5 during
cooling must be smaller than the maximum thermal expansion
coefficient .epsilon. within the limit of the tensile strength of
the spacer 5. When the expression (4) is satisfied, breakage of the
spacer 5 during cooling can reliably be prevented.
When the spacer is secured to the surface of the cathode substrate
in a state in which the predetermined tension is not added to the
spacer, excessive distortion and/or breakage takes place. If a
plate-like spacer having a thermal expansion coefficient which is
smaller than that of the cathode substrate by 5.times.10.sup.-7
/.degree. C. and a width of 50 .mu.m and a length of 100 mm in a
state in which heating to 450.degree. C. is performed after the
spacer has been secured, distortion not larger than 1 mm occurs
when heating is performed, as shown in FIG. 10. When the foregoing
heat treatment is performed after the cathode substrate to which
the spacer has been secured and the anode substrate have been
disposed opposite to each other, the plate-like spacer undesirably
projects through the gap between the adjacent electron emission
units. As a result, the fluorescent member disposed on the anode
substrate is sometimes critically damaged. In the foregoing case,
the FED undesirably displays a defective image.
The FED according to the foregoing embodiment are structured to
satisfy the expressions (1), (2), (3) and (4). Therefore,
distortion and breakage can be prevented if the heat treatment and
the cooling test are performed. Therefore, a state in which a
predetermined tension is applied can be maintained. As a result,
the spacers 5 can accurately be disposed even if the heat treatment
and the cooling test are performed. Therefore, the fluorescent
members 6 disposed on the anode substrate 4 of the FED can be
protected from a damage. As a result, the FED according to the
present invention is able to reliably display a satisfactory image
free from lowering of the brightness.
As described above, the image display apparatus according to the
present invention has the structure that the two ends of the spacer
is secured to at least either of the anode substrate or the cathode
substrate in a state in which a tension is added to the spacer in
the lengthwise direction of the spacer. Therefore, the image
display apparatus according to the present invention is able to
prevent distortion and breakage of the spacer thereof. Moreover,
the spacers can be disposed at required positions. Therefore, the
image display apparatus according to the present invention is free
from lowering of the brightness of a displayed image and enabled to
have satisfactory strength against high pressure.
The method of manufacturing the image display apparatus according
to the present invention is structured such that the spacers are
joined in a state in which a predetermined tension is added to each
spacer in the lengthwise direction of the spacer. Therefore, the
spacers can accurately be joined.
Although the invention has been described in its preferred form and
structure with a certain degree of particularity, it is understood
that the present disclosure of the preferred form can be changed in
the details of construction and in the combination and arrangement
of parts without departing from the spirit and the scope of the
invention as hereinafter claimed.
* * * * *